Should I Attempt to Replace the ABS Hydraulic Control Unit Myself?

[xntryk1]

The leaky ABS pump on my '95 Legacy L wagon needs to be replaced. I've already got the part (Nippon 26731AA200) and now I'm wondering if this is something I should tackle myself or leave to the so-called 'experts'. Looking at the Chilton manual, it doesn't seem as easy as simply replacing the part and bleeding the system. There's a whole 12-point list of instructions for "bleeding the hydraulic unit" that involves "applying AV electrical signals to the solenoid", etc., etc. and so on. 

 

My question is, is all that really necessary? the unit shown in Chilton is different from mine. Has anybody replaced one of these units and if so, how big of a hassle was it?

 

I can handle relatively simple repairs. But when it starts getting into esoteric electrical stuff, I'm out of my element...

Edited January 2, 2016 by xntryk1

[Fairtax4me]

It's no different than bleeding the brake system normally.

 

Couple tricks. Before installing the unit pour brake fluid into all the ports and rock it around some to get some of the air out.

When removing the lines from the old unit, cap the ends so all the fluid doesn't drain out of the lines and the master cylinder.

Once the new unit is in the car, loosen the line nuts while you bleed out the supply lines first, tighten those then loosen the lines that go to the wheels one at a time while bleeding them. Gravity bleed them first by leaving the nuts loose until most of the air bubbles stop. Then pressure bleed them by having someone press the brake pedal and holding it, then crack the line nuts loose one at a time.

Once you've got all the air out of the unit, then bleed the calipers in a cris-cross fashion.

[987687]

If you press the brake pedal down and use a stick or whatever between the pedal and the seat it will keep fluid from draining out of the master cylinder. Holding the pedal down closes the port between the MC and the reservoir keeping fluid from draining out. Remember it'll keep your brake lights on, so unhook the battery or remove the horn fuse, which the brake lights are also on.

[porcupine73]

I'm not sure if your model ABS had it but I know on '00obw the ABS could be put into sequence control by connecting certain pins on the diagnostic connector. I think it said that made it cycle the pressure valves and pump to help bleed itself out and stuff. Here it is

Edited January 3, 2016 by porcupine73

[xntryk1]

Thanks, porcupine73. Mine looks exactly like the ABS-2E unit pictured in that pdf. I believe this is the section you're referring to:

 

Sequence Control
Sequence Control is the name of a mode in which the system automatically runs the HCU pump motor and cycles the solenoid valves. The Sequence Control actions help to purge air out of the hydraulic control unit.
To activate Sequence Control, proceed as follows:
• With the ignition off, jumper both the “L” and “K” terminals in the ABS check connector to ground.
• Turn the ignition switch to On and watch the ABS warning lamp.
• When the lamp goes off, immediately press and hold the brake pedal.
• The ECU now runs the pump and cycles all the solenoid valves. You will hear and feel this happening.
• When you hear the pump stop, you know Sequence Control is done.
• Release the brake pedal and turn the ignition to Off.
When you have completed Sequence Control, bleed all four brake circuits again. Top off the master cylinder reservoir after bleeding each circuit. Then road test the vehicle at low speed. Apply the brakes hard two or three times to make sure the brakes are working properly.

 

That doesn't look TOO complicated. But my first question would be, where is the "ABS check connector"? And how do I "jumper" those 2 terminals to ground?

Edited January 3, 2016 by xntryk1

[porcupine73]

On my 00obw I don't remember which ABS it has but the connector was under the dash. It was the same connector where you ground some pin to make it flash out any error codes. The connector itself had two grounding wires on it that could be used. I did learn however not to just stick the grounded wire pins randomly into the connector trying to find the right combination since that blew the fuse. I didn't see that connector diagram in my files but I did find this one which I remember saving because it's kind of funny picturing a professional asking the customer if they would describe the sound as more a gong gong or a bong bong

Edited January 3, 2016 by porcupine73

[xntryk1]

Ha! I can relate to that graphic. But as far as I can tell, my '95 Legacy L wagon doesn't have that kind of connector under the dash. More likely, I don't know exactly what I'm supposed to be looking for...

[Fairtax4me]

http://www.ultimatesubaru.org/forum/topic/79577-abs-diagnosis-connector-location/

 

Pic there.

Its a black 6 pin plug. Two open spade terminals are ground pins, taped in the same harness.

Pin 3 is the K terminal

Pin 6 is the L terminal

 

It looks giant sized in the picture but that connector is really only about 3/4" wide.

Edited January 3, 2016 by Fairtax4me

[xntryk1]

Thank you, Fairtax4me. I'll save those pics for if/when I ever get to that point. Also, you mentioned something about capping the ends of the brake lines after removing them from the HCU. What would I use to cap them with?

 

Also, thank you 987687 for the tip on the brake pedal. I've also read that putting a 2x4 under the pedal will keep it from going all the way to the floor. 

 

Another stupid question - for bleeding the brakes at each wheel, will it require jacking the car up and removing each wheel? Or is there an easier way (hopefully)?

[987687]

You can reach in there with a wrench and get to the bleeders, usually 10mm in the front 8mm in the back. It's kind of a pain on a Legacy because they're low, but possible.  DO NOT BREAK THE BLEEDERS OFF!!!!!! Especially the back ones are small and like to break off if they're at all rusty, go slow, use heat, use PB blaster, whatever. Don't break them. Trust me. If the bleeder is missing the little condom cap thing and no fluid is coming out, take it all the way out and use a piece of wire to clean the dirt out of it.

Edited January 3, 2016 by 987687

[xntryk1]

Sounds good, 987687! Thanks to you guys and your wealth of knowledge, this job is looking more and more like something I might be able to tackle by myself - even with my limited tools and experience.  

[Fairtax4me]

I have a handful of rubber vacuum line caps that I use. You can get them at most parts stores for a few bucks for a variety pack.

 

You can also use the little silicone thread protector caps for screws. I've seen them at some hardware stores in the specialty fasteners section.

[xntryk1]

Aha! I should have known there were such things out there. Thanks again, Fairtax4me!

[xntryk1]

Just thought I'd add a (hopefully) final note on this thread. Before I got around to replacing the ABS pump, believe it or not, it magically fixed itself! After 6 months (in my ownership) and a little over a gallon of brake fluid dumped in, the leak just suddenly stopped one day. And this happened a couple months ago. Ever since then, the reservoir level has stayed topped-off (by itself) and the brakes seem to work perfectly.

 

So I dunno... it's the strangest thing. Leaks don't normally fix themselves. I'm not trying to look a gift horse in the mouth, but It makes me wonder what the heck was going on in that ABS pump? And what could have possibly happened to fix it? I haven't the slightest idea. But for the record, that's what happened... 

[vasy]

Where on the ABS unit did it leak from?